Msg#: 4669515 posted 9:21 pm on May 8, 2014 (gmt 0)
In most cases, upgrading your hosting involves moving to a new server. It sounds like the move in your case wasn't handled in a way that the DNS propagation was seamless. It's likely that when your DNS does fully propagate, your traffic should come back and that no rankings will be lost. I would monitor this, though, and check with your host. Also, check your server configuration on the new box, which might change some of your settings.
To give you some more understanding of the topic... for that seamless transition between between servers, you should have had a copy of your site up and running on the new server as well as on the old (something which you can't always do if you have a dynamic site), as changing your server changes your IP number. Thus, someone (in this case, probably your host) also changed your DNS to a new IP, and it takes a while for that new address to propagate. How your DNS and hosting is set up would affect how smooth your transition was and how long complete propagation might take.
Here's a thread that discusses most of the issues of moving to a new host... very similar to changing to a new server... and also includes a link to the Matt Cutts article on the topic, which is our standard reference here....